TVC vs. active pre?

I'm using a Bent Audio NOH in my system, and love the sound - it's detailed, open, dynamic, coherent, musical and very immediate.

Whenever I talk to amp designers however, the universal preference seems to be for active preamps. My feeling is that if there are no interfacing issues between the pre and the power amp (sufficient voltage drive, no impedance or capacitance problems) that an active pre can't "add quality" to the signal. As far as I can tell, an active preamp provides buffering and gain. Absent any need for these, I don't see what benefits it can provide.

Is my assessment incomplete? Are the recommendations for active preamps simply based on the avoidance of potential interfacing issues in unknown systems?

I understand that a good active may beat a poorly implemented passive, but given good design/build in both situations, what would it take for an active to beat a good passive, especially a TVC? And specifically, has anyone gone from a TVC to an active? If so, what were the system issues that prompted the change?
In a pure technical sense I agree with you - every thing else being equal - no difference. However the proper use of a passive is a hair-shirt affair and commands some knowledge (actually fairly extensive knowledge) and dilligence to execute properly - not for the convience orientated or faint of heart. Personally, liking midrange bloom and a better sence of "air" as I do (i.e. tubes) I wouldn't go that route, but I'd put one with a remote in my tape loop for volume control.
The job of the line stage in a preamp is to similtaneously provide volume control and also control the effects of the interconnect cable. A depressingly large number of preamps (especially tube preamps) fail at this task. Passive volume control systems are usually even worse when it comes to the latter task, though often better at the former.

The concept of the TVC is nice in that one should be able to have both a good volume control as well as cable control, but in practice the effects of the transformer are quite noticeable and the difference in sound from one volume control setting to another (which is a problem that plagues passive units) is still there.

The only way to get around the buffering (to interface to the cable and load) issue in a passive is to build the volume control into the amplifier. This is not always practical, as one is still stuck with the fact that the quality of the control remains critical. Good volume controls (usually some form of multiposition switch) are fairly large; semiconductor style controls (often used in remote volume controls) don't as yet sound right.

'Right' is a relative term; the more transparent your system the more these comments will make sense.
My limited experence with passives in my system has been very favorable towards them. I think they have the kind of midrange quality that tube lovers talk about..only better. I have listened to the Placette passive (very good) and I owned the Bent TVC for about a year (also very good). Do I think that an active pre-amp can better the Placette or Bent, sure I do..but at much cost. I plan to bring a passive back into my system in the future as I only sold mine to upgrade elsewere in my system on short notice.


After living with several well respected tube preamps such as offerings from BAT, Audible Illusions, Cary, JJ Electronics, and Kora, I now have a custom preamp using the Mark I version of the TX-102 transformer. There is no comparison regarding bass extension, dynamics and transparency, the TVC has it all over the competition. You might give up a slight bit of midrange bloom, but this is very close. The TVC actually has a more fleshed out midrange than some tube preamps, while retaining greater resolution. I also heard the Placette in my system and my buddy's too, not even in the same ballpark as a TVC.

I agree that the performance of any passive linestage will be system dependent. I have heard my preamp in another system and it didn't perform nearly as well as it does with my gear. So caveat emptor, but for me the TVC is great.

Philosophically, it would seem that if you already have enough gain in your system, a passive should just pass on an exact copy of the magnificent sound produced by your source components attenuated down to the intensity of your desires. While it ain't necessarily that simple, I am finding that passive linestages can be very, very good in practice.

The theoretical problem with passives is that they can give a frequency response to your system which depends on their setting. For example, at low volumes they might be great, but as the setting is increased they might cause the system to attenuate the higher frequencies. This can be due to the interaction of the passive's output impedance with the capacitance of the interconnects and the input impedance of the amplifier. The output impedance of the source can also play a role. So, a passive won't necessarily work well in every system. (Note: There are many schemes to get around these effects and if you do a search of the 'Gon archives or the Audio Asylum a wealth of information will come up.)

My experience is similar to what's posted above. I am going through the process of comparing a resistive passive with active linestages. The resistive passive (ladder) is my reference.

The preliminary conclusion in my (all tube) system is that the passive is very tough (but not impossible, so far) to beat. I have it up against a CJ Premiere 16 Series II and a Nagra PL-P. It might be rolling off the very high frequencies at some settings, but not by much and possibly this can be controlled by system matching the impedance of the passive, interconnects, and amplifier input.

The differences in performance between the above three linestages can be quite dependent on upstream (i.e. software, cartridge, and phonoamp) and downstream (interconnects and amplifier). If you are going through system changes (like I am at the present), or you play through a variety of sources, I can see where a passive might not be flexible enough. And, of course, it also depends on how revealing your system is.

I have not yet tried a transformer-based passive (I've got one coming) and I'm not finished testing and developing yet, but the fact that a DIY set of resistors, 24-position switch, and aluminum box with RCA connectors for about $400 is giving big-name linestages (for >20x the $'s) a run for their money should say something!

Like it's really worth taking the time to investigate whether it's going to work for you in your system.
I have an all tubed and vinyl only system and I have gone from active preamp to built-in passive TVC ( TX-102) in my custom made phono stage. One very noticeable differnce is increased dynamics, especially coming out from my Quad ESL 63 speakers, which is not known for it's dynamics. Also, frequency extremes do not seem suppressed. I would love to do a comparison on the same phono stage with TVC and resistor-based volume control.
OK folks,

Have you ever gone from active pre to built-in volume control card inside of your poweramp?

If not, than THAT I consider as BEST option for any system that negates ANY impedance matching, compression or roll-offs of any kind that may or maynot occur within the transfer from active preamp unit to the power amplifier.

Technically for such "carded" power amplifier you will only need an input selector which is certainly passive or if you wish remote controlled.

The volume controll card is to be installed either between input stages or between output and driving stage. This way the older amps were made.
I appear to have answered my own question. A new friend strongly encouraged me to try his Audion Premier line stage. Last night, four hours after I plugged it in I agreed to buy it.

In my system the Audion provided better dynamics, resolution and articulation than the NOH, and not by a narrow margin either.

It seems now that, theoretical issues aside, it still comes down to implementation.